We present a high-resolution Mg/Ca reconstruction of tropical Atlantic sea surface temperatures (SSTs) spanning the last 2000 years using seasonally representative foraminifera from the Cariaco Basin. The range of summer/fall SST over this interval is restricted to 1.5°C, while winter/spring SST varies by 4.5°C over the same time period suggesting that boreal winter variations control interannual SST variability in the tropical North Atlantic. Antiphasing between the two data sets, including a large divergence in the seasonal records circa 900 Common Era, can be explained by changes in Atlantic meridional overturning circulation and associated changes in surface/subsurface temperatures in the tropical North Atlantic as well as resultant changes in trade wind belt location and intensity. A statistically significant but nonlinear relation exists between reconstructed winter/spring temperatures and solar variability.

However, solar variability leads the Cariaco temperature record by 25-40 years, suggesting the linkage between solar variability and tropical SSTs is driven by relatively slow marine processes rather than faster atmospheric ones. The first half of the Mg/Ca record challenges this hypothesis, as the relationship between the Cariaco record and solar variability seems to break down, but that may be attributed to the inconsistency of G. bulloides as either a surface or subsurface temperature indicator. It is also possible that the early portion of the Mg/Ca record may have been dominantly forced by something other than solar variability, with the solar correlation only becoming relevant later in the record. The data sets distinctly diverge in 1950, possibly as a result of anthropogenic influences dominating the more recent tropical SST signal or another shift in the G. bulloides proxy.